1. Field of the Invention
The present invention relates to a technology for automatically assigning terminal IDs that are identifiers for uniquely identifying each of a plurality of terminal units on a network having a "1" to "n" connecting function, such as a CATV network, in the system a center unit and the terminal unit being able to bidirectionally communicate.
2. Description of the Related Art
In recent years, a network communication system that accomplishes a bidirectional service such as a telephone service or a VOD (Video On Demand) service, has been developed using an existing CATV network that performs "1" to "n" connections. In such a communication system, since a plurality of terminal units are connected to one center unit, each terminal unit should be uniquely assigned respective identifier (terminal ID).
In a conventional bidirectional communication system such as the PHS (Personal Handyphone System), terminal IDs of terminal units are normally assigned when they are shipped from their factories.
However, in this system, since terminal IDs should be assigned uniquely throughout the world, their ID numbers become long. In addition, the ID number writing process and management of the terminal IDs become complicated.
In a conventional system for automatically assigning terminal IDs, the TEI (Terminal Endpoint Identifier) assigning system is known. In the TEI system, an ISDN (Integrated Services Digital Network) exchange that is a center unit assigns IDs to BRI (Basic Rate Interface) terminal units. In this system, as shown in FIG. 1, a BRI terminal unit sends a UI (Unacknowledged Information) message that represents a TEI assignment request to the ISDN exchange. The ISDN exchange assigns an TEI to the BRI terminal unit, stores the assigned TEI, and sends a UI message that acknowledges that the TEI has been assigned to the BRI terminal unit. When the BRI terminal unit receives the acknowledgment message, the BRI terminal registers the TEI of the message. Thereafter, the BRI terminal unit communicates with the center unit using the assigned TEI. In this manner, TEIs can be automatically assigned to individual BRI terminal units.
The TEI assigning system has been defined with respect to a basic rate interface of the ISDN having two B channels and one D channel. The system deals with up to eight BRI terminal units that can be connected to one "2B+D" interface. Thus, in the above-described system in which a terminal unit sends a terminal ID assignment request to the center unit, when the number of terminal units increases, the probability of which assignment requests contend rises. However, the above-described system does not provide a mechanism for solving such contention. Thus, the above-described system cannot be applied for a bidirectional communication system that assigns unique terminal IDs to many terminals.